Fuel pumps for vehicles rapidly pressurize an amount of fuel delivered or drawn from a low-pressure fuel supply, such as a tank or reservoir, to a fuel delivery system for an internal combustion engine. Depending on the type of fuel delivery system used, i.e. a carburetor, a throttle body injection system, a port injection system, or a direct fuel injection system, the fuel may be delivered to or directed into the engine under relatively low- or high-pressure. For example, a fuel injection system typically requires fuel to be delivered at much higher pressures than does a carburetor. High-pressure (HP) fuel pump assemblies used with Spark Ignition Direct Injection (SIDI) engines in particular typically utilize fuel rail pressures of approximately 150 to 200 bar,
Combustible fuel may be pressurized to a sufficiently high level of pressure using a high-pressure (HP) fuel pump system or assembly. Such a HP fuel pump assembly typically operates as a demand-style pump assembly, i.e. a pump assembly having an output pressure and flow rate that vary in accordance with certain engine operating parameters such as load, speed, and/or temperature. Demand-style pump assemblies may be configured as either a “return” or a “returnless” design, depending on the respective presence or absence of a dedicated or separate fuel return line. That is, a returnless fuel pump assembly is characterized by the presence of a fuel feed line for delivering fuel to a portion of a pumping chamber within a pump bushing, and also by the absence of a dedicated fuel return line for returning an amount of unused fuel from the pumping cavity back to the tank/reservoir.